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  • POP3 and IMAP comparison for Email downloading

    Posted on kempware Comment on the AskWoody Lounge

    Home Forums Networking – routers, firewalls, network configuration POP3 and IMAP comparison for Email downloading

    • This topic has 41 replies, 13 voices, and was last updated 3 weeks ago.
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      • #2257304 Reply
        kempware
        AskWoody Plus

        I’m looking for a technical comparison of the POP3 and IMAP protocols for downloading email to a client such as MS Outlook.

        In my environment, and that of quite a few others we deal with, people like to use the Outlook client to download and manage their email, particularly from a provider such as gmail. Outlook offers greater usability and function than the browser based methods of accessing gmail accounts. Sometimes, we have multiple people in different locations wanting to access the same gmail account. If you configure Outlook to download the emails to different computers you can run into all sorts of issues.

        To better understand and advise them on this, I’d like to know how Outlook (and presumably other email clients) decide what emails are to be downloaded each morning when the computer is started. Outlook is very good at knowing what has been downloaded before and what hasn’t. But how does it work? How does it know when to start downloading from? Where is the information stored regarding what has previously been downloaded?  It can’t simply be date/time based. Gmail offers good anti-spam capability and it will quarantine spam emails in the spam folder and you need to check it from time to time. If you move an email out of the spam folder and back to the inbox, even if the spam email was received several weeks ago, Outlook is smart enough to know this email needs to be downloaded even though lots of emails received after this date have already been downloaded. How does it know this?

        When concurrent access to emails is needed, it has been suggested we could use IMAP instead of POP3 to download emails, as IMAP seems to just reflect (synchronise) what Outlook sees compared to what is actually held in the gmail mailbox. But IMAP raises other issues in my mind. What if i cleanup the gmail mailbox say in order to keep under the free gmail storage limit (eg. say where google drive is also used for that account and the data volume builds up you might want to delete old emails). What impact does that have on what Outlook can see, does it still see the old deleted emails or not? In the POP3 world, Outlook creates .pst files whereas it creates .ost files for IMAP accounts. These .ost files are not so easily managed, archived, able to be moved between systems etc etc.

        So, has anybody ever done such a technical comparison of how email downloading works for POP3 and IMAP ?

        Any help or pointers to published articles, would be appreciated.

        Thanks!

        peter

         

        2 users thanked author for this post.
      • #2257315 Reply
        Paul T
        AskWoody MVP

        You don’t need a technical document for what is basically a simple process.

        POP3

        1. Download mail based on user settings.
        2. Record ID of email downloaded in local database.
        3. Delete email from server if user setting requires. If you want email in multiple machines you need to leave it on the server for a minimum time that guarantees the other machine(s) will download it.

        Advantages
        Less server storage required if mail is deleted from the server.
        Less network traffic.
        Easy management of shared mailboxes

        IMAP

        1. Synchronize email folders to the local machine based on user settings – not all folders may be synchronized.

        Advantages
        Mail is always backed up because nothing is deleted from the server, unless you move it to trash.
        Easy mail replacement on a new machine, the whole lot is synched.

        4 users thanked author for this post.
      • #2257427 Reply
        kempware
        Guest

        Hi,

        Thank-you Paul for your thoughts.  But is it really as simple as that? My understanding from speaking with the users is that if there are multiple pc’s configured to download into outlook from the same gmail account, then there are many examples where emails get downloaded to one but not the other of the pc’s. That behaviour is inconsistent i think with the idea that there is a “local database” by which you presumably mean the ID’s are stored in the .pst files (which are totally seperate and unrelated). I figured there must be something happening at the gmail mail server to note that an email had already been downloaded and therefore not to download it again. And no, they have not configured to delete from the mail server after downloading.  🙂

        And as for using IMAP, i think you are confirming that if emails get deleted from gmail then they will no longer be visible from Outlook too even though they had previously been downloaded.

         

      • #2257514 Reply
        mn–
        AskWoody Lounger

        In the POP3 world, Outlook creates .pst files whereas it creates .ost files for IMAP accounts. These .ost files are not so easily managed, archived, able to be moved between systems etc etc.

        … right, .ost is offline storage for a synced IMAP account.

        If you copy mail from the IMAP account into a local-only archive folder, Outlook puts it into a .pst file even so. (“Move” to somewhere outside the IMAP session is actually copy followed by deletion of the original.)

        I’d like to know how Outlook (and presumably other email clients) decide what emails are to be downloaded each morning when the computer is started. Outlook is very good at knowing what has been downloaded before and what hasn’t. But how does it work? How does it know when to start downloading from? Where is the information stored regarding what has previously been downloaded? It can’t simply be date/time based.

        Well it actually can be simply date/time based, it’s just that usually it isn’t…

        IMAP gives unique, persistent, index numbers to each message in the mailbox. It also assigns them “flags” such as ‘\Seen’, ‘\Answered’, …’\Recent’ … Then the mail client requests a list of messages, checks that against a local database (the .ost file in case of Outlook) and sees which numbers it already has locally, and typically matches those with a criteria and then downloads a set.

        Then the client sends back things like flag changes, new messages (typically into Drafts or Sent)… when able.

        Given the specific behaviour of the \Recent flag, I’d say using it to determine whether to download a message or not isn’t very useful, but I’m not at all surprised that Outlook would do so anyway.

        Also IMAP can get just parts of a message.

        It’s possible to do IMAP without any local content storage at all. That means the client downloads only those pieces it’ll display or process. This is quite uncommon these days… but some dedicated “unread mail exists in mailbox” notifier apps do exist.

        Outlook is often set to only sync full messages that arrived within the last year. That means, if the server has older messages, they’re listed but not downloaded for offline use.

        (IIRC also if you manage to get an IMAP mailbox open while your clock is badly off, some applications didn’t download messages that have arrived in the future…)

        1 user thanked author for this post.
      • #2257531 Reply
        Vincenzo
        AskWoody Lounger

        If tried and was unable to get Gmail to work via POP3 in Outlook 2016, even though I had enabled the setting in Gmail to allow it. It completed the setup successfully but would not download any mail. I will be interested to see if you are successful.

      • #2257753 Reply
        Paul T
        AskWoody MVP

        there are many examples where emails get downloaded to one but not the other of the pc’s

        Most likely one of the PCs has POP3 set to delete mail after download, so PCs connecting later see nothing new. One mis-configured POP3 PC messes up the whole show.

        cheers, Paul

        2 users thanked author for this post.
        • #2257928 Reply
          mn–
          AskWoody Lounger

          … or in case of IMAP, client triggers a download on the \Recent flag. Yes, it’s sort of stupid to do so; yes, I do distinctly recall seeing that happen anyway (years ago), just didn’t remember which client it was…

      • #2257978 Reply
        36dups
        AskWoody Lounger

        IMAP vs POP is more about the client experience rather than technical merits.

        As noted by others IMAP is technically more advanced because it’s a true client-server based architecture.  POP is really just a dedicated email download process from a single INBOX location.

        If you want to have more than a single client accessing the mail store then IMAP is better because each client can show what the server holds, or a subscribed subset of the structure on the server.  There should be no difference between what each clients shows the user.  IMAP provides for “PUSH” updates so if the client supports IMAP idle then when messages arrives at the server they are notified in short order, although this does require a continuous network link.  POP is a “poll the storage server” process and hence is only checking on a schedule, although IMAP can be used the same way.

        Most mobile platforms have vendor supported email clients that support both protocols, and almost all support the IMAP push notification process.  If not then Andoid users can install the open source K9 Mail client and it support all the IMAP features their chosen server supports.  Both POP and IMAP support “only headers” mode so the body of the message is not retrieved by the client until it is needed.

        Unfortunately the MS Outlook client application, not to be confused with the mobile Outlook applicaiton, and IMAP have a less than harmonious relationship that has varied with each release of Outlook.  It mostly works.  If Outlook becomes confused (OST or PST corruption) then synchronisation with IMAP back end can break badly (to the point of not working at all).  Fixing it is normally as simple as deleting the local outlook data store and letting a re-sync happen.  This is rarely the case with POP based configurations, any corruption for a POP PST file needs the venerable scanpst to work it’s magic.

        Your going to have to evaluate what is the most appropriate mechanism for the usage you have in mind.  Professionally the IMAP path is normally more work although the benefits mainly outweigh the issues for just a single system POP is a good choice.

        The one thing to note is that with IMAP you must ensure the storage capacity to hold all of the emails on the server is configured.  Smaller hosted implementations with IMAP may have lower than acceptable limits on total mailbox size and as IMAP hosted folders sit on the server they consume space.  POP (set to remove after 14 days) ensures that the storage space is always well below the limits.

        1 user thanked author for this post.
      • #2268244 Reply
        anonymous
        Guest

        There is one major disadvantage to IMAP. If the e-mail account is entered by a hostile third party, all of the messages can be deleted and the trash folder can be emptied. In most cases, those messages will be lost forever. In a POP account, the messages will have been downloaded to the client, so their content will have been saved somewhere other than the server. For this reason, I only use POP.

        2 users thanked author for this post.
        • #2268253 Reply
          Paul T
          AskWoody MVP

          Unless you have “delete from server after download” turned on – often the default setting.

          Backup is the only true recovery mechanism.

          cheers, Paul

          1 user thanked author for this post.
          • #2268406 Reply
            anonymous
            Guest

            “Delete from server after download” makes no sense for IMAP. The whole point is to keep everything on the server so that the messages can be consulted from other devices. If the messages are to be deleted as soon as they’re downloaded, simply use POP.

            As for backup, how could the IMAP message store be backed up? (POP, yes, but IMAP?)

            regards, AndyA

            • #2268618 Reply
              Paul T
              AskWoody MVP

              Re-reading your post I see you may be suggesting malicious email access from the internet. That’s a very specific case of data loss, but a simple backup of your PC would save the required mail – and you should backup your PC anyway.

              cheers, Paul

              • #2269260 Reply
                anonymous
                Guest

                < That’s a very specific case of data loss >

                Yes, and one that can be disastrous if the data is unavailable.

                AFAIK, a simple backup of my PC will not work for IMAP. Once the messages are deleted from the email server, how can the messages be recovered on the PC?

                regards, AndyA

              • #2269277 Reply
                mn–
                AskWoody Lounger

                AFAIK, a simple backup of my PC will not work for IMAP. Once the messages are deleted from the email server, how can the messages be recovered on the PC?

                If they HAD been synchronized to local email client and would have been usable in offline mode when you took the backup, then restoring the email client’s data and starting it in offline mode should result in them being available from the now-restored cache.

                Traditionally mail clients liked to store everything in a single large blob (.pst or whatever), but each message in its own file is also out there in some clients if you look for it. (Configuration option in recent version of Thunderbird, for example – “Maildir format”)

                There are also dedicated email backup solutions, even client-side.

                (Me? I run Linux at home anyway. I use a dedicated tool to sync all my IMAP accounts into a single large Maildir hierarchy under $HOME locally, run a local IMAP server with $HOME/Maildir as its per-user message store, and then point my actual mail client at that. I use a snapshotting filesystem so can recover accidental deletions as individual files from snapshots, and…)

              • #2269795 Reply
                anonymous
                Guest

                If they HAD been synchronized to local email client and would have been usable in offline mode when you took the backup, then restoring the email client’s data and starting it in offline mode should result in them being available from the now-restored cache.

                This doesn’t sound very likely. Most, if not all, of the time, someone using an email client opens the client in online mode to retrieve new messages. If the IMAP store has been maliciously deleted, that’s it, then. The messages are gone.

                This is why I do not use IMAP. I use POP. If my message store is deleted on the server, I’ve retained my email history.

                It’s surprising that so little attention is paid in this thread (and elsewhere) about this IMAP risk that is avoided with POP.

                regards, AndyA

              • #2269862 Reply
                mn–
                AskWoody Lounger

                If the IMAP store has been maliciously deleted, that’s it, then. The messages are gone.

                Sane IMAP clients also check for local data consistency. If the local storage isn’t found at all, it should be caught as an invalid local copy and won’t be synced to server.

                With POP3, there’s only one “authoritative” storage location ever. If that’s on your PC and you have a disk failure or whatever, hope you had good backups…

                Restoring IMAP local storage from backup is not significantly different from restoring POP local storage from backup, and with IMAP you have also the option of doing the restore on the server side.

                So yeah, in practice catastrophic data loss is much more common with POP than with IMAP.

              • #2272217 Reply
                anonymous
                Guest

                Of course, thorough backup practices are a prerequisite for data restoration in case of use of a POP account. But from your last message, that’s also true for IMAP accounts.

                Sane IMAP clients also check for local data consistency. If the local storage isn’t found at all, it should be caught as an invalid local copy and won’t be synced to server.

                I’ve never ever heard of this. Could you provide a link to support this behavior by any IMAP client? (Connection to server successful, data deleted, local data left untouched.)

                Restoring IMAP local storage from backup is not significantly different from restoring POP local storage from backup,

                Again, I’m unfamiliar with this. AFAIK, IMAP local storage, such as an Outlook .OST, cannot be opened on a second computer. It’s not a backup. It’s a copy of the server. If the server synchs with the .OST and the .OST is emptied, the data is lost.

                You’ve stated that the local IMAP storage will be unaffected by deletion of the server, but I don’t (yet) believe this to be the case. You’ve also stated that the local IMAP storage is as good a backup as local POP storage, yet that’s clearly not the case. (An Outlook .OST file cannot be opened on another computer.)

                BTW, I’ve seen this problem. An IMAP account is compromised, the data is deleted on the server, the message store is gone forever.

                regards, AndyA

              • #2273125 Reply
                mn–
                AskWoody Lounger

                Could you provide a link to support this behavior by any IMAP client? (Connection to server successful, data deleted, local data left untouched.)

                … er, no. Didn’t specify that at all. I was talking about the case where it goes, connection to server successful / local data invalid or missing -> do not delete from server …

                You’ve stated that the local IMAP storage will be unaffected by deletion of the server, but I don’t (yet) believe this to be the case.

                Of course it’s unaffected UNTIL NEXT SYNC. And at sync, what you need to do with it is to make sure any old delete operations aren’t reapplied to what was restored from backup.

                With IMAP you have the option of doing the restore on either client or server side, with approximately the same caveats.

                You’ve also stated that the local IMAP storage is as good a backup as local POP storage, yet that’s clearly not the case. (An Outlook .OST file cannot be opened on another computer.)

                That’s a limitation of Outlook, not a limitation of IMAP. Do NOT mistake the limitations of any one implementation as general limitations of the protocol – Outlook on the client and MS Exchange on the server have notable limits that the protocol doesn’t have.

                Thunderbird for one example manages that just fine with local data generated on another computer, and can work just fine with roaming profiles in a Windows domain login setup… except maybe for the impatient, as it syncs the roaming profile with the domain’s specified file server at login/logout.

                There are other such IMAP clients too.

                1 user thanked author for this post.
        • #2269866 Reply
          cyberSAR
          AskWoody Plus

          Little real world experience here. Have a client that was using IMAP. They had an issue with a bank transfer of $250,000. The bank received a request from them to change the account number they were wiring the money to. That had occurred occasionally before, and the bank never double-checked, but this time the girl at the bank had a gut feeling and decided to check with them. Sure enough, it was bogus.

          Going through server logs we noted where the perp had hacked into their webmail app about 1 month prior. Client had used a very poor password for years. He had access to a year’s worth of emails, contracts, signatures, contacts etc. He waited for the right moment and created an email declaring they had made a mistake on the account number to transfer to. It used language, signatures and of course the email address consistent with my client’s and was sent from their server. Fortunately he didn’t get away with it.

          They now use POP3 with rigorous backups and keep everything in-house and mail is NOT left on the server. Plus they now have much better passwords 🙂

          4 users thanked author for this post.
          • #2269934 Reply
            mn–
            AskWoody Lounger

            Going through server logs we noted where the perp had hacked into their webmail app about 1 month prior. Client had used a very poor password for years. He had access to a year’s worth of emails, contracts, signatures, contacts etc.

            … Well yeah, that’ll be bad.

            Once had to help clean up after someone had fallen for a phising attack. On a cloud-integrated account… cloud-storage malware-sharing spam outflow to all contacts, yuck.

            (Apparently taken from the cloud-integrated address book instead of mail header harvesting, though.)

            Was a lot quicker to notice though. The police paperwork was a bit nasty though. (GDPR notification, names and contact details stolen…)

            Something wrong about it too if signatures could just be stolen like that, surely a private key should not be kept anywhere externally accessible…

            They now use POP3 with rigorous backups and keep everything in-house and mail is NOT left on the server. Plus they now have much better passwords 🙂

            Leaving mail on the server is still the lesser part, compared to having the mail/groupware server in-house and inside the corporate firewall. No random webmail logins from wherever.

            Yes, this is one of the major issues with big cloud setups. Nothing quite like old-fashioned firewalls and in-house servers if security is what you’re after.

            1 user thanked author for this post.
            • #2269944 Reply
              cyberSAR
              AskWoody Plus

              Not a corporate / in-house server. Shared server, and by signatures I mean their logo’s and text signatures. No private keys. Very simple setup for a small biz.

              • #2269953 Reply
                36dups
                AskWoody Lounger

                @cybersar, a very real life warning to others to be vigilant.  From your description it would have made little difference with the selection of IMAP vs POP as with even using POP the attacker could still siphon off messages before the local client had downloaded them.  The necessity to poll for POP emails leaves a window of opportunity to capture the inbox message state and as each client has it’s own list of what email message have been unread there would be no traces except that in the POP server logs an entry showing the attacker accessing the account.

                Unfortunately poor security hygiene is a problem for many, regardless of business size, and the choice of a less than secure password has at oft times been the downfall of many.  Both POP and IMAP current reliance on password based authentication makes 2FA a non starter. 🙁

              • #2270078 Reply
                cyberSAR
                AskWoody Plus

                36dups you are correct of course that if the perp gets access via pop or imap and they are patient enough the same could have occurred. The issue I have with IMAP was that they had access to years of emails once logged in.

          • #2270000 Reply
            Paul T
            AskWoody MVP

            POP3 is of no value if the malicious user has mail on all the time and doesn’t delete messages from the server. They will then have a copy of all email.

            Proper passwords, 2FA and restrictions based on network / IP is the only way to secure online systems.

            cheers, Paul

      • #2268261 Reply
        Chris B
        AskWoody Plus

        Also a user experience comment. I moved from POP top IMAP several years ago and far prefer it. I access email on three devices, a PC via Outlook 2010, a Samsung tablet via Samsung email and a Moto phone via Gmail. All work well, with the following specific comments:

        Outlook always gets the full email content, but quite often stalls (see 36dups’s comment). That may be old age of the software (the PC is new), or the size of the email file (1.5GB). All it takes to sort it is a restart of Outlook, which is a minor irritation.

        Samsung is pretty good on current emails, but sometimes I have to get it to re-poll the server a  few times to pull down the older emails.

        Gmail is also pretty good, but it has the irritating habit of not removing emails I have moved or deleted from the in box,  sometimes for days or weeks.

        I deal with the hack/delete problem by backing up my PST file every night on my PC.

        Chris
        Win 10 Pro x64 Group A

      • #2268262 Reply
        glnz
        AskWoody Plus

        This is a great thread, kempware and all others here.

        So this is what I have to do, and your views will be appreciated:

        For years, I was viewing my personal email on one PC – an XP machine with Outlook Express (which I miss).  It was all POP3 with the setting to leave a copy of the original email on the server.  I never used IMAP.  A year ago, still in that XP machine, I moved ALL of my emails to Outlook 2003 and stopped using Outlook Express.  Still POP3 and leave a copy of email on the server.  My older in and sent emails were and are in folders in Oultook Express and now Outlook 2003 – only the past year is in Inbox and Sent on Outlook 2003.

        My personal incoming email has always been [myname]@verizon.net.  Verizon moved that to AOL a few years ago, and there are issues with AOL being the server for my email.  The worst is that the emails re-download over and over, now almost every day.  I’m pretty sure the problem is with AOL, not the Outlook 2003, as the problem does not happen with a second email account on that Outlook that is not hosted by AOL.  To reduce the duplicate downloads, I have been going to AOL on a browser and moving the emails into Archive on AOL.   So my AOL Inbox now only holds a few emails (or none) at any moment.

        But now I want to ditch the XP machine.  I have a newer Dell Optiplex 7010 running Win 10 Pro 64-bit (currently version 1909) and Office 365 Home 64-bit.  I have not yet set up its Outlook.  When I set up that Outlook, I know that it will prompt me first to connect to a different email account, [myname]@outlook.com, which I hardly use, but I will let it do that.  I do not know whether it will do that as IMAP or POP3.

        Then, when I test to see that [myname]@outlook.com is working, I will add my original [myname]@verizon.net account to to that Outlook 365.  Before I do that, I will go into AOL and move my remaining Inbox emails to Archive so that the Outlook 365 will only download new emails going forward.  I am strongly tempted to continue as POP3 with leave a copy of message on server.  But then, finally for the first time in my life, I will connect my iPhone to this personal email, and there I think I will make it IMAP.  (My iPad is already connecting to [myname]@verizon.net, apparently as IMAP, even though my Outlook 2003 on my XP machine connects to the same email as POP3.)

        What do you think?

        • #2269951 Reply
          36dups
          AskWoody Lounger

          @glnz with what your suggesting ti should work fine.

          If you do not want to add the “@outlook” address you can elect to skip it when creating the account.  If you have 365 you can use the control panel mail applet to add the required accounts before event starting the outlook desktop application.  Using POP or IMAP as required for each account.

          When you moved from Outlook Express did you migrate the emails over to an Outlook PST file?  If not it MAY be sensible do do so before decommissioning the XP boxen.  That way you can have the email history storage  as an Archive folder in the 365 (local to the new Win10 system only).

          As long as any connected POP client is set to NOT remove the emails from the server the IMAP connected client will still see all of the emails.  If you set a single POP client to remove the messages after a delay then only the messages still on the server will be available to any IMAP client.  A workable solution as long as you do not starting moving messages into non-inbox server side folders using the IMAP client (as a POP client will never see these non-inbox folders).

        • #2270001 Reply
          Paul T
          AskWoody MVP

          I will connect my iPhone to this personal email, and there I think I will make it IMAP

          This requires the same amount of space on your phone as on the server. Either stick to POP3 or use the email app from AOL.

          cheers, Paul

      • #2268270 Reply
        bbearren
        AskWoody MVP

        I have stayed with POP3 since the beginning with Outlook Express, and for a simple reason.

        I have three email accounts that I use with Outlook 365 (now Microsoft 365) and all three have unlimited server storage for my email.  One account is my own website hosting company.

        All the accounts are setup to leave email on the server.  That amounts to free cloud storage/backup for my email.  I could uninstall, then reinstall Microsoft 365 and years worth of email would download to the new Outlook setup with the same accounts.

        I have multiple folders in my Outlook email, and a single folder on my email servers.  Outlook sorts incoming email to the appropriate folder using a set of rules.  With IMAP I would have to setup those folders on the server.  I’d rather keep that on my end.

        Create a fresh drive image before making system changes/Windows updates, in case you need to start over!
        "When you're troubleshooting, start with the simple and proceed to the complex."—M.O. Johns
        "Experience is what you get when you're looking for something else."—Sir Thomas Robert Deware

      • #2268271 Reply
        Chris B
        AskWoody Plus

        I have multiple folders in my Outlook email, and a single folder on my email servers.  Outlook sorts incoming email to the appropriate folder using a set of rules.  With IMAP I would have to setup those folders on the server.  I’d rather keep that on my end.

        @bbearren No you wouldn’t! When I transferred over to IMAP, the server picked up all my Outlook folders and their contents in the initial sync, and kept them synced thereafter. No manual labour involved!

        Chris
        Win 10 Pro x64 Group A

        • #2268382 Reply
          mn–
          AskWoody Lounger

          That depends entirely on how it’s configured.

          Outlook rules to sort mail into local folders is not synced back to server even if you’re using IMAP or MAPI for the server connection, and certainly not with POP.

          1 user thanked author for this post.
          • #2268399 Reply
            Chris B
            AskWoody Plus

            @mn I agree. The way I have it the movement of emails to folders, whether by rules or manually, is done by Outlook but once the move has happened, the IMAP server will mirror the change.

            Chris
            Win 10 Pro x64 Group A

            1 user thanked author for this post.
            • #2269950 Reply
              36dups
              AskWoody Lounger

              The use of the Outlook client local rules and IMAP are compatible as @mn and @chris-b have noted.  The rule can select either a local folder or a folder that is available via IMAP.  That’s an all client side process.  If you are considering this then the same functions could be performed by server side add on (assuming the email service provider supports it).  It provides for a rich mail filtering process on the system that holds the mail store.  It really depends on the server side implementation but it’s agnostic to either POP or IMAP as the message retrieval process.  If your using a Linux based email server then Sieve is most likely available, an Exchange based mail system has a similar feature when using the Outlook client to setup rules.

              The problem is that POP does not support folders so in real terms the use of Sieve is limited to accessing the mail store with IMAP (or using some web based direct mail store access mechanism).

              @mn, mail store access via MAPI provides a whole new raft of possibilities for application developers but no so much for the end user.  Access to an Exchange server via IMAP for an Outlook client would work only for emails. Accessing the same system using MAPI would get ALL of the Exchange groupware features like calendaring, o-o-o replies, shared folders.  From the OP’s original text I did not think that MAPI was part of the desired mix, although it may be an option.

              • #2270239 Reply
                mn–
                AskWoody Lounger

                @mn, mail store access via MAPI provides a whole new raft of possibilities for application developers but no so much for the end user. Access to an Exchange server via IMAP for an Outlook client would work only for emails. Accessing the same system using MAPI would get ALL of the Exchange groupware features

                … well, depends on which version of Exchange you have.

                Used to be that you could have IMAP access to calendar, contacts and whatnot. See for example, https://docs.microsoft.com/en-us/exchange/configure-calendar-options-for-imap4-exchange-2013-help … “Set-ImapSettings -Server CAS01 -CalendarItemRetrievalOption iCalendar”

                … once upon a time I did interesting things with that.

                But, can’t have that with O365 / Exchange Online, and wouldn’t be surprised if it was removed from on-premises Exchange 2016 too.

      • #2268410 Reply
        bryash
        AskWoody Plus

        I have been using POP from the days of Outlook Express and moved to Outlook in about 2003.  I simply copy my .pst files from computer to computer, manually set up the email accounts in the new Outlook and point Outlook to the location of the pst files on the new computer.  This shows the old emails immediately and I proceed to download the new emails on whatever schedule I choose.  I synchronise my desktop and laptop computers by simply backing up the pst files from one to the other, though when travelling (when I use my laptop) I direct the emails I wish to keep on my computer to a travelling folder to simplify synchronising it back to my desktop on my return.

        I often use Outlook’s edit email function to clean up emails I wish to keep while the original emails are left on the servers (I use gmail accounts for their excellent spam filters) and periodically check online for any messages incorrectly sent to spam or trash.

        With all this I use IMAP on my phones and this dual use appears to work well for me.  I have never had issues setting up POP on Outlook though you have to be careful but once it works it works consistently.

        Hope this is helpful

      • #2268550 Reply
        anonymous
        Guest

        I use POP because if I delete messages on my phone or notepad they are not deleted on the server as they would be with IMAP. I do not like a large list of messages on my phone or notepad. I leave that to my PC to keep. I only delete the messages when online with Gmail, otherwise they are always there unless 30 days has elapsed and then those over 30 days are deleted. It works for me. I tried IMAP and discovered that when I deleted a message on my phone that I had not downloaded to my PC that it was gone and not able to retrieve it. I have folders on my PC that I keep my important messages in. I do not have that kind of room on my notepad. My phone has more room than my notepad but it would be hard to sort through on such a small screen. 6 inches versus 27 inch monitor. So, POP is mine and I wish they would update it to like POP4 but keep what I like as far as being able to delete from one device but not from the server.

        • #2268619 Reply
          Paul T
          AskWoody MVP

          Why don’t you keep a limited number of emails in your Inbox and then set IMAP to only sync the Inbox to your phone?

          cheers, Paul

      • #2269011 Reply
        anonymous
        Guest

        Does anyone know how to remove emails from your email client, in this case, Outlook 365, while leaving them on the server? I’m trying to avoid clutter on the computer.

        • #2269070 Reply
          mn–
          AskWoody Lounger

          Yes – this is entirely specific to the application in question.

          I believe Outlook has, in the Application settings, a slider that you can set to “all”, “last year”, “last month” etc. as the period from which it keeps local copies. There may also be more advanced settings for this.

          Other applications may have anything from no such setting at all to much more detailed filter features.

          • #2269102 Reply
            anonymous
            Guest

            Thanks MN. I found the settings. I can set it for as little as 1 month to as long as “all.” The question remains, if I set it to say, 1 month, will the messages disappear from my computer after 1-month but remain on the server? I neglected to mention that I’m using imap.

            Thanks again for your insights.

            • #2269131 Reply
              mn–
              AskWoody Lounger

              Yes, they should all remain on the server, and are accessed transparently from there if you’re online.

              Also they don’t disappear from Outlook completely, because otherwise they’d show up as “new” messages on next sync. The header listings are still cached, just the message bodies are unavailable while offline.

              Also, this is assuming everything works correctly. Outlook has had bugs related to this in the past.

              And, last time I checked there was no easy way to inspect exactly what is cached and what isn’t.

      • #2269906 Reply
        oldfry
        AskWoody Plus

        POP3 on GMAIL:

        I download my mail using POP3 from multiple GMAIL accounts at once to Outlook 2016 successfully.   I have GMAIL automatically delete the mail on the server after download.   I realize I need to backup the local PST files and do so monthly at least.   This restricts me to a single PC for email, unlike IMAP.

        GMAIL’s POP3 behavior is that the received mail is moved to the trash and really deleted after 30 days.   So I have a temporary backup on the server.

        GMAIL’s SMTP behavior is to leave all sent mail on the server.   For that problem, I have to log into each mail account and delete the mail manually, if I wish.    I am not aware of an option to delete sent mail on just the server automatically, but wish there was.

        I choose not to use IMAP, because I don’t want my email to reside on a server I don’t control.

        For Google mail accounts, you need to use 2FA with a secure method to help prevent a breach from a web login.   But the 2FA is ignored when sending/receiving email in Outlook 2016, so I never have to provide a password for my multiple GMAIL accounts.   There is a one time procedure to generate an application password for each account.    But not sure how secure application passwords are.

        1 user thanked author for this post.
        • #2269911 Reply
          Microfix
          AskWoody MVP

          Been using pop3 since the era of x486 PC’s, only on PC’s.
          I’ve also backed up locally over decades, and removed from server on retrieval as a standard setup. IMAP is only used (separate email account) for my mobile phone.

          | Win8.1 Pro x64 | Linux Hybrids x86/x64 | Win7 Pro x86/x64 Offline |
          1 user thanked author for this post.
          • #2269916 Reply
            cyberSAR
            AskWoody Plus

            You and I think alike. I also don’t use my throwaway gmail accounts for anything sensitive or important. Chaps me that I have to even have them but it is what it is (I hate that phrase but it fits) 🙂

      • #2270079 Reply
        geekdom
        AskWoody Plus

        Consider storing all mail you wish to keep in local folder; then delete the online mail.

        If, for any reason, you close a mail account, you will still have your stored correspondence.

        G{ot backup} TestBeta
        offline▸ Win7Pro SP1 x64 Storage
        online▸ Win10Pro 1909.18363.900 x64 i5-9400 RAM8GB HDD Firefox79.0b5 Windows{Image/Defender/Firewall}
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